Various systems and in particular, hydraulic systems, require pressure control of a fluid flow used in operation of components of the system. Pressure control valves are implemented for a variety of functions such as prohibiting system pressure from exceeding a predetermined pressure limit and maintaining a set pressure in the system.
A conventional type of pressure control valve is a pilot operated relief valve used to control a high pressure or high fluid flow feed to a hydraulic circuit or device, such as a pump. The pilot operated relief valve generally includes an inlet, a piston positioned on a seat of the inlet, a chamber positioned above the piston, a control orifice in communication with the chamber, and a pilot section that contains a spring-loaded poppet and sets a maximum system pressure. A flow path from an outlet of the control orifice on top of the piston leads to the pilot. Fluid used by the pilot section may return to a reservoir. In operation, fluid flows through the inlet to the hydraulic circuit and through the control orifice to the chamber. The fluid also travels to the spring-loaded poppet, where the fluid is blocked. When pressure is too low to unseat the spring-loaded poppet, pressure is the same on both sides of the piston and a spring holds the piston in a normally closed position.
When pressure exceeds the maximum system pressure, the spring-loaded poppet open slightly to allow a small amount of fluid to pass to the reservoir. However, the fluid passing the spring-loaded poppet also flows through the control orifice such that flow to the reservoir may be blocked. As pressure increases, the spring-loaded poppet in the pilot section is opened enough to allow a greater amount of flow than the flow through the control orifice such that pressure in the chamber decreases. When the pressure imbalance exceeds a predetermined value, the piston moves towards the decreased pressure and opens a flow path to the reservoir. When the system pressure decreases, the spring-loaded poppet reseats itself. A disadvantage of the pilot operated relief valve is that they generally operate at a lower maximum pressure and leakage than may occur at the valve seat during high pressure applications.
A direct acting pressure reducing valve may be used as an alternative to using a pilot operated valve in controlling high pressure in a hydraulic system. Direct acting pressure reducing valves respond more rapidly to pressure buildup in comparison with the pilot operated relief valve. The direct acting pressure reducing valve is generally controlled with a solenoid. However, a disadvantage of the direct acting pressure reducing valve is that in a high-pressure application, requirements for the solenoid may demand a solenoid that is disadvantageously large in size.